The present application claims priority under 35 USC 119 to Japanese Patent Application No. 2001-021670 filed on Jan. 30, 2001 the entire contents thereof is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an air pressure detection device for a wheel, and particularly to an air pressure detection device for a wheel having a structure in which a reception antenna is inserted by molding into a resin fender.
2. Description of Background Art
An air pressure detection device for a wheel which makes it possible for the driver to recognize the air pressure of a tire even during operation of the vehicle, there is known, for example, as set forth in Japanese Patent Laid-open No. Hei 10-44762, entitled xe2x80x9cTire Air Pressure Alarm Device.xe2x80x9d
As set forth in FIG. 1 of Japanese Patent Laid-open No. Hei 10-44762, a tire air pressure alarm device is set forth in which a valve stem 10 (symbols used in the publication are used here) is fitted to a wheel rim 1. A case 2 is disposed at a lower portion of the valve stem 10. A transmission unit 7 including a pressure detection portion 3, a signal processing circuit 4 and an electric cell 5 is contained in the case 2.
In order to receive an electromagnetic wave emitted from the transmission unit of such a tire air pressure alarm device, a reception antenna is needed. Generally, a reception antenna is incorporated in the receiver or an electric wire connected to the receiver.
However, in the case where the antenna incorporated in the receiver is used as the reception antenna, the position of the antenna depends on the position where the receiver is fixed. Necessarily, the position of the reception antenna is limited to the position where the receiver can be fixed. Where the position of the reception antenna is farther than the receiver, there is the problem that the sensitivity of the reception antenna is lowered.
In addition, since the reception antenna is incorporated in the receiver, the size of the reception antenna is limited to the size of the receiver. Therefore, when the receiver is reduced in size, the reception antenna cannot be enlarged in size, resulting in a problem that the sensitivity of the reception antenna cannot be enhanced.
Further, where an electric wire connected to the receiver is used as the reception antenna, a jig for fixing is needed for fixing the wire. Therefore, projection of the jig or the like occurs, leading to the problem that the appearance is spoiled.
In order to solve the above problems, it is an object of the present invention to provide an air pressure detection device for a wheel which has a reception antenna that is pitched widely, has high sensitivity, and has a good appearance.
In order to attain the above object, an air pressure detection device for a wheel according to the present invention includes an air pressure sensor for detecting the air pressure of a tire and a transmission means for emitting pressure information detected by the air pressure sensor provided on the side of a wheel of the vehicle. A reception means is provided on the side of the vehicle body. A reception antenna of the reception means is inserted by molding into a fender formed of an insulating resin.
Since the reception antenna of the reception means is inserted by molding into the fender formed of an insulating resin, the distance from the transmission means fitted to the air pressure sensor to the reception antenna is reduced, so that reception sensitivity is enhanced. In addition, since the reception antenna can be pitched substantially to the size of the fender, the reception sensitivity is also enhanced. Further, since jigs for fixing the antenna are needless, a reduction in the number of component parts can be contrived.
The present invention includes an embodiment wherein the reception antenna is a metallic antenna. Since the reception antenna is metallic, the connection of an electric wire leading to the receiver can be easily connected by soldering or the like, so that wiring is easy.
The present invention includes an embodiment wherein the reception antenna is an electrically conductive resin antenna. Since the reception antenna is made of a resin, it is possible to set the thermal expansion of the antenna to be substantially the same as that of the resin forming the fender. Therefore, internal stress between the inserted by molding antenna and the fender due to temperature variation will not be generated, so that the antenna can have a long useful life even when used in an environment with severe temperature changes.
Further scope of applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.